Immune and proliferative cellular responses to Helicobacter pylori infection in the gastric mucosa of Mexican children

BACKGROUND: Helicobacter pylori infection occurs mostly during childhood, but few studies on this age group have addressed the innate immune and the proliferative response to this infection. Mexico has a high H. pylori prevalence in children, but a low risk of gastric cancer. The aim of this work was to study the cellular responses of the gastric mucosa to this infection in Mexican children. METHODS: Antral and corpus gastric biopsies were obtained from 44 H. pylori-infected children (mean age 12 +/- 3.2 years) and 44 uninfected children (mean age 10 +/- 3 years). Mucosal cellular responses were studied by immunohistochemistry, using anti-Ki67 antibodies for proliferation studies, antihuman tryptase for mast cells, and antihuman CD68 for macrophages. T and B lymphocytes were stained with a commercial integrated system. The intensity of cellular responses was estimated histologically using the software KS300. RESULTS: Epithelium proliferation and infiltration of macrophages and T and B lymphocytes were significantly higher in H. pylori-infected than in uninfected children. A balanced increase of CD4, CD8, and CD20 lymphocytes was observed in infected children. However, activated mast cells were decreased, and infiltration of neutrophil and mononuclear cells was low. Epithelial proliferation was associated with polymorphonuclear infiltration but not with infiltration of macrophages or lymphocytes. Inflammation and proliferation was higher in CagA (+)-infected children. CONCLUSIONS: Mexican children respond to H. pylori infection with a low inflammatory response, a balanced increase of T and B lymphocytes, and a high regenerative activity.     

Adoptive transfer of splenocytes in SCID mice implicates CD4+ T cells in apoptosis and epithelial proliferation associated with Helicobacter pylori-induced gastritis

Helicobacter pylori causes severe, rapidly progressive gastritis in severe combined immunodeficient (SCID) mouse recipients of congenic splenocytes. The H. pylori-infected and uninfected C57BL/6J and recipient SCID mice were evaluated to detect CD4+ and CD8+ T cells, B cells, apoptotic epithelial cells, and epithelial cell proliferation at postinoculation weeks 5, 6, 8, and 12. Serum was evaluated for anti-H. pylori IgG and IgM. In all H. pylori-infected mice, gastric CD4+ cell scores were increased, compared with scores for uninfected controls. Recipient mice differed, however, according to the source of the transferred CD4+ cells. The CD4+ cell scores for recipients of splenocytes from H. pylori-infected (immune) donors were indistinguishable from those for wild-type donor mice at all time points. In contrast, gastric mucosal CD4+ cell scores did not become significantly high until two weeks after transfer (postinoculation week 6) in recipients of cells from uninfected (na?ve) donors. Gastric epithelial apoptosis and the gastric epithelial proliferation zone were significantly (P < 0.05) increased in infected recipient and donor, compared with non-recipient and uninfected mice at postinoculation week 12. Results indicated that CD4 cells are sensitized in vivo and migrate to the gastric mucosa where they induce gastritis in response to H. pylori antigens. Influx of CD4 cells and gastritis are correlated with epithelial proliferation and apoptosis, and suggest that CD4-dependent H. pylori gastritis leads to epithelial damage with attendant proliferative and metaplastic responses.     

Expression of B7-H1 on gastric epithelial cells: its potential role in regulating T cells during Helicobacter pylori infection

Helicobacter pylori infection is associated with gastritis, ulcers, and gastric cancer. The infection becomes chronic as the host response is unable to clear it. Gastric epithelial cells (GEC) play an important role during the host response, and their expression of class II MHC and costimulatory molecules such as CD80 and CD86 suggests their role in local Ag presentation. Although T cells are recruited to the infected gastric mucosa, they have been reported to be hyporesponsive. In this study, we detected the expression of B7-H1 (programmed death-1 ligand 1), a member of B7 family of proteins associated with T cell inhibition on GEC. Quantitative real-time RT-PCR revealed that B7-H1 expression increased significantly on GEC after H. pylori infection. Western blot analysis showed that B7-H1 expression was induced by various H. pylori strains and was independent of H. pylori virulence factors such as Cag, VacA, and Urease. The functional role of B7-H1 in the cross talk between GEC and T cells was assessed by coculturing GEC or H. pylori-infected GEC with CD4+ T cells isolated from peripheral blood. Using blocking Abs to B7-H1 revealed that B7-H1 was involved in the suppression of T cell proliferation and IL-2 synthesis, and thus suggested a role for B7-H1 on the epithelium as a contributor in the chronicity of H. pylori infection.     

Evidence for Transepithelial Dendritic Cells in Human H. pylori Active Gastritis

Background:  Despite extensive experimental investigation stressing the importance of bacterial interaction with dendritic cells (DCs), evidence regarding direct interaction of Helicobacter pylori or its virulence products with DCs in the human gastric mucosa is lacking.
Methods:  Human gastric mucosa biopsies, with or without H. pylori infection and active inflammation, were investigated at light and electron microscopy level with immunocytochemical tests for bacterial products (VacA, urease, outer membrane proteins) and DC markers (DC-SIGN, CD11c, CD83) or with the DC-labeling ZnI₂-OsO₄ technique. Parallel tests with cultured DCs were carried out.
Results:  Cells reproducing ultrastructural and cytochemical patterns of DCs were detected in the lamina propria and epithelium of heavily infected and inflamed (but not of normal) mucosa, where DC luminal endings directly contact H. pylori and take up their virulence products. Cytotoxic changes (mitochondrial swelling, cytoplasmic vacuolation, autophagy) were observed in intraepithelial DCs and reproduced in cultured DCs incubated with H. pylori broth culture filtrates to obtain intracellular accumulation of VacA and urease. Granulocytes were also seen to contact and heavily phagocytose luminal H. pylori , while macrophages remained confined to basal epithelium, though taking up bacteria and bacterial products.
Conclusion:  Human DCs can enter H. pylori -infected gastric epithelium, in association with other innate immunity cells, to take up bacteria and their virulence products. This process is likely to be important for bacterial sensing and pertinent immune response; however, it may also generate DC cytotoxic changes potentially hampering their function.     

Increased production of matrix metalloproteinases in Helicobacter pylori-associated human gastritis

BACKGROUND AND AIMS: Helicobacter pylori infection results in an active, chronic inflammation of the gastric mucosa. Previous studies have highlighted the importance of matrix metalloproteinases (MMPs) in diseases involving mucosal inflammation, prompting us to investigate MMP activity in H. pylori-induced gastritis. METHODS: Gastric biopsies were obtained from H. pylori-infected and uninfected volunteers, and MMP activity was assessed using substrate gel electrophoresis. MMP production was also evaluated by immunohistochemistry and real time-polymerase chain reaction. In parallel, tissue inhibitors of MMPs (TIMP) levels and TIMP-MMP complexes were examined in corresponding tissues using enzyme-linked immunosorbent assays and Western blotting. Finally, MMP production by gastric macrophages was determined after stimulation with H. pylori. RESULTS: Antral mucosa of H. pylori-infected subjects demonstrated a 19-fold higher MMP-9 activity than that of uninfected individuals. MMP-2 was present at lower levels, but was also increased in H. pylori-infected individuals, while there was no difference in the total levels of TIMP-1 and TIMP-2 between the groups of volunteers. Significant numbers of MMP-9-containing cells were only found in the H. pylori-infected antral mucosa. Tissue-resident macrophages were significantly increased in H. pylori-infected individuals, and double-staining showed MMP-9 colocalized to macrophages. Furthermore, gastric macrophages secreted MMP-9 in response to H. pylori bacteria. A corresponding 10-fold increase of gene expression of MMP-9 was seen in patients infected with H. pylori compared to uninfected individuals. CONCLUSIONS: Helicobacter pylori infection results in a substantial increase in MMP-9 and MMP-2 activity in the gastric mucosa, probably contributed to in large part by tissue-resident macrophages, while no changes were seen in the TIMP levels. The net increase in gastric MMP activity is likely to contribute to tissue damage during H. pylori-associated gastritis.     

Comparison of mucosal B- and T-cell responses in Helicobacter pylori-infected subjects in a developing and a developed country

Helicobacter pylori is highly endemic in developing countries, but comparatively little is known about mucosal immune responses to H. pylori in these settings. Therefore, we have compared B- and T-cell responses, with a focus on the gastrointestinal mucosa, in H. pylori-infected adults in a developing (Bangladesh) and a developed (Sweden) country. We found comparable numbers of CD19(+) B cells and CD4 (+)T cells and similar levels of H. pylori-specific IgA antibodies in gastric mucosa from Bangladeshi and Swedish volunteers. However, about threefold higher numbers of CD19(+) B cells and 12-fold increased levels of H. pylori-specific IgA antibodies were found in the duodenum of Bangladeshi subjects. The gastric and duodenal immune responses in Bangladeshi asymptomatic carriers and duodenal ulcer patients were comparable. Bangladeshi subjects had about twofold lower titers of H. pylori-specific IgA and IgG antibodies in the circulation compared with Swedish volunteers. In conclusion, our findings suggest that Bangladeshi individuals have comparable gastric immune responses, but lower systemic antibody responses to H. pylori, compared with Swedish volunteers. Increased inflammation is present in the duodenum of Bangladeshi volunteers, maybe as a result of frequent exposure to enteric infections in these individuals.     

Host response to Helicobacter pylori infection before initiation of the adaptive immune response

Helicobacter pylori persistently colonizes the human stomach. In this study, immune responses to H. pylori that occur in the early stages of infection were investigated. Within the first 2 days after orogastric infection of mice with H. pylori, there was a transient infiltration of macrophages and neutrophils into the glandular stomach. By day 10 postinfection, the numbers of macrophages and neutrophils decreased to baseline levels. By 3 weeks postinfection, an adaptive immune response was detected, marked by gastric infiltration of T lymphocytes, macrophages, and neutrophils, as well as increased numbers of H. pylori-specific T cells, macrophages, and dendritic cells in paragastric lymph nodes. Neutrophil-attracting and macrophage-attracting chemokines were expressed at higher levels in the stomachs of H. pylori-infected mice than in the stomachs of uninfected mice. Increased expression of TNFalpha and IFNgamma (Th1-type inflammatory cytokines) and IL-17 (a Th17-type cytokine) was detected in the stomachs of H. pylori-infected mice, but increased expression of IL-4 (a Th2-type cytokine) was not detected. These data indicate that a transient gastric inflammatory response to H. pylori occurs within the first few days after infection, before the priming of T cells and initiation of an adaptive immune response. It is speculated that inappropriate waning of the innate immune response during early stages of infection may be a factor that contributes to H. pylori persistence.     

CD4+CD25+ suppressor T cells regulate pathogen induced inflammation and disease

A key suppressor role has recently been ascribed to the natural CD4+CD25+ regulatory T cells (Treg), the removal of which leads to the development of autoimmune disease and aggravated pathogen-induced inflammation in otherwise normal hosts. The repertoire of antigen specificities of Treg is as broad as that of naive T cells, recognizing both self and non-self antigens, enabling Treg to control a broad range of immune responses. Although widely acknowledged to play a role in the maintenance of self-tolerance, recent studies indicate that Treg can be activated and expanded against bacterial, viral and parasite antigens in vivo. Such pathogen-specific Treg can prevent infection-induced immunopathology but may also increase the load of infection and prolong pathogen persistence by suppressing protective immune responses. This review discusses the role of Treg in the prevention of exaggerated inflammation favoring chronicity in bacterial or fungal infections and latency in viral infections. Special attention is given to the role of Treg in the modulation of gastric inflammation induced by Helicobacter pylori infection. Findings in both experimentally infected mice and humans with natural infection indicate that Treg are important in protecting the H. pylori-infected host against excessive gastric inflammation and disease symptoms but on the negative side promote bacterial colonization at the gastric and duodenal mucosa which may increase the risk in H. pylori-infected individuals to develop duodenal ulcers.     

Helicobacter pylori urease binds to class II MHC on gastric epithelial cells and induces their apoptosis

Infection by Helicobacter pylori leads to injury of the gastric epithelium and a cellular infiltrate that includes CD4+ T cells. H. pylori binds to class II MHC molecules on gastric epithelial cells and induces their apoptosis. Because urease is an abundant protein expressed by H. pylori, we examined whether it had the ability to bind class II MHC and induce apoptosis in class II MHC-bearing cells. Flow cytometry revealed the binding of PE-conjugated urease to class II MHC+ gastric epithelial cell lines. The binding of urease to human gastric epithelial cells was reduced by anti-class II MHC Abs and by staphylococcal enterotoxin B. The binding of urease to class II MHC was confirmed when urease bound to HLA-DR1-transfected COS-1 (1D12) cells but not to untransfected COS-1 cells. Urease also bound to a panel of B cell lines expressing various class II MHC alleles. Recombinant urease induced apoptosis in gastric epithelial cells that express class II MHC molecules, but not in class II MHC- cells. Also, Fab from anti-class II MHC and not from isotype control Abs blocked the induction of apoptosis by urease in a concentration-dependent manner. The adhesin properties of urease might point to a novel and important role of H. pylori urease in the pathogenesis of H. pylori infection.     

Natural Killer Cell Receptor+ T‐Lymphocytes in Normal and Helicobacter pylori‐Infected Human Gastric Mucosa

Background: Helicobacter pylori infection is associated with development of chronic inflammation and infiltration of immune cells into the gastric mucosa. As unconventional T‐lymphocytes expressing natural killer cell receptors are considered to play central roles in the immune response against infection, a study investigating their frequencies in normal and H. pylori‐infected gastric mucosa was undertaken. Materials and Methods: Flow cytometry was used to quantify T‐cells expressing the natural killer cell markers CD161, CD56, and CD94 in freshly isolated lymphocytes from the epithelial and lamina propria layers of gastric mucosa. Thirteen H. pylori‐positive and 24 H. pylori‐negative individuals were studied. Results: CD94⁺ T‐cells were the most abundant (up to 40%) natural killer receptor‐positive T‐cell population in epithelial and lamina propria layers of H. pylori‐negative gastric mucosa. CD161⁺ T‐cells accounted for about one‐third of all T‐cells in both compartments, but the lowest proportion were of CD56⁺ T‐cells. Compared with H. pylori‐negative mucosa, in H. pylori‐infected mucosa the numbers of CD161⁺ T‐cells were significantly greater (p = .04) in the epithelium, whereas the numbers of CD56⁺ T‐cells were lower (p = .01) in the lamina propria. A minor population (< 2%) of T‐cells in both mucosal layers of H. pylori‐negative subjects were natural killer T‐cells, and whose proportions were not significantly different (p > .05) to those in H. pylori‐infected individuals. Conclusions: The predominance, heterogeneity, and distribution of natural killer cell receptor‐positive T‐cells at different locations within the gastric mucosa reflects a potential functional role during H. pylori infection and warrants further investigation.     

Helicobacter pylori, T cells and cytokines: the "dangerous liaisons"

Helicobacter pylori infection is the major cause of gastroduodenal pathologies, but only a minority of infected patients develop chronic and life threatening diseases, as peptic ulcer, gastric cancer, B-cell lymphoma, or autoimmune gastritis. The type of host immune response against H. pylori is crucial for the outcome of the infection. A predominant H. pylori-specific Th1 response, characterized by high IFN-gamma, TNF-alpha, and IL-12 production associates with peptic ulcer, whereas combined secretion of both Th1 and Th2 cytokines are present in uncomplicated gastritis. Gastric T cells from MALT lymphoma exhibit abnormal help for autologous B-cell proliferation and reduced perforin- and Fas-Fas ligand-mediated killing of B cells. In H. pylori-infected patients with autoimmune gastritis cytolytic T cells infiltrating the gastric mucosa cross-recognize different epitopes of H. pylori proteins and H+K+ ATPase autoantigen. These data suggest that peptic ulcer can be regarded as a Th1-driven immunopathological response to some H. pylori antigens, whereas deregulated and exhaustive H. pylori-induced T cell-dependent B-cell activation can support the onset of low-grade B-cell lymphoma. Alternatively, H. pylori infection may lead in some individuals to gastric autoimmunity via molecular mimicry.     

Intestinal and splenic T cell responses to enteric Listeria monocytogenes infection: distinct repertoires of responding CD8 T lymphocytes

Listeria monocytogenes is an intracellular bacterium that causes systemic infections after traversing the intestinal mucosa. Clearance of infection and long term protective immunity are mediated by L. monocytogenes-specific CD8 T lymphocytes. In this report, we characterize the murine CD8 T cell response in the lamina propria and intestinal epithelium after enteric L. monocytogenes infection. We find that the frequency of MHC class Ia-restricted, L. monocytogenes-specific T cells is approximately 4- to 5-fold greater in the lamina propria than in the spleen of mice after oral or i.v. infection. Although the kinetics of T cell expansion and contraction are similar in spleen, lamina propria, and intestinal epithelium, high frequencies of Ag-specific T cells are detected only in the lamina propria 1 mo after infection. In contrast to MHC class Ia-restricted T cells, the frequency of H2-M3-restricted, L. monocytogenes-specific T cells is decreased in the intestinal mucosa relative to that found in the spleen. In addition to this disparity, we find that MHC class Ia-restricted CD8 T cells specific for a dominant L. monocytogenes epitope have different TCR V beta repertoires in the spleen and intestinal mucosa of individual mice. These findings indicate that the intestinal mucosa is a depot where L. monocytogenes-specific effector CD8 T cells accumulate during and after infection irrespective of immunization route. Furthermore, our results demonstrate that CD8 T cell populations in these two sites, although overlapping in Ag specificity, are distinct in terms of their repertoire.     

Induction of CD8+ regulatory T cells in the intestine by Heligmosomoides polygyrus infection

This study determined whether Heligmosomoides polygyrus induces intestinal regulatory T cells. Splenic T cells proliferate strongly when cultured with anti-CD3 and antigen-presenting cells (APC). Lamina propria T cells from mice with H. polygyrus mixed with normal splenic T cells from uninfected mice inhibited proliferation over 90%. Lamina propria T cells from mice without H. polygyrus only modestly affected T cell proliferation. The worm-induced regulatory T cell was CD8+ and required splenic T cell contact to inhibit proliferation. The regulation also was IL-10 independent, but TAP-dependent, suggesting that it requires major histocompatibility complex (MHC) class I interaction. Additional studies employed mice with transgenic T cells that did not express functional TGF-beta receptors. The lamina propria T regulator inhibited proliferation of these transgenic T cells nearly 100%, suggesting that TGF-beta signaling via the T cell was not required. CD8+ T cells were needed for worms to reverse piroxicam-induced colitis in Rag mice (T and B cell deficient) reconstituted with IL-10-/- T cells. Thus H. polygyrus induces a regulatory CD8+ lamina propria T cell that inhibits T cell proliferation and that appears to have a role in control of colitis.     

Role of cyclooxygenase-2 in Helicobacter pylori- induced gastritis in Mongolian gerbils

Cyclooxygenase (COX)-2 expression is induced in the gastric mucosa of Helicobacter pylori-infected patients, but its role remains unclear. We examined the effects of NS-398 and indomethacin on gastric pathology in H. pylori-infected Mongolian gerbils. COX-1 was detected in both normal and H. pylori-infected mucosa, whereas COX-2 was expressed only in the infected mucosa. PGE(2) production was elevated by H. pylori infection, and the increased production was reduced by NS-398, which did not affect PGE(2) production in normal mucosa. Indomethacin inhibited PGE(2) production in both normal and infected mucosa. Hemorrhagic erosions, neutrophil infiltration, lymphoid follicles, and epithelium damage were induced by H. pylori infection. NS-398 and indomethacin aggravated these pathological changes but did not increase viable H. pylori number. H. pylori-increased production of neutrophil chemokine and interferon-gamma was potentiated by NS-398 and indomethacin. Neither NS-398 nor indomethacin caused any pathological changes or cytokine production in normal animals. These results indicate that COX-2 as well as COX-1 might play anti-inflammatory roles in H. pylori-induced gastritis.     

Subepithelial myofibroblasts are novel nonprofessional APCs in the human colonic mucosa

The human gastrointestinal mucosa is exposed to a diverse normal microflora and dietary Ags and is a common site of entry for pathogens. The mucosal immune system must respond to these diverse signals with either the initiation of immunity or tolerance. APCs are important accessory cells that modulate T cell responses which initiate and maintain adaptive immunity. The ability of APCs to communicate with CD4+ T cells is largely dependent on the expression of class II MHC molecules by the APCs. Using immunohistochemistry, confocal microscopy, and flow cytometry, we demonstrate that alpha-smooth muscle actin(+), CD90+ subepithelial myofibroblasts (stromal cells) constitutively express class II MHC molecules in normal colonic mucosa and that they are distinct from professional APCs such as macrophages and dendritic cells. Primary isolates of human colonic myofibroblasts (CMFs) cultured in vitro were able to stimulate allogeneic CD4+ T cell proliferation. This process was dependent on class II MHC and CD80/86 costimulatory molecule expression by the myofibroblasts. We also demonstrate that CMFs, engineered to express a specific DR4 allele, can process and present human serum albumin to a human serum albumin-specific and DR4 allele-restricted T cell hybridoma. These studies characterize a novel cell phenotype which, due to its strategic location and class II MHC expression, may be involved in capture of Ags that cross the epithelial barrier and present them to lamina propria CD4+ T cells. Thus, human CMFs may be important in regulating local immunity in the colon.     

Helicobacter pylori vacuolating cytotoxin inhibits activation-induced proliferation of human T and B lymphocyte subsets

Helicobacter pylori are Gram-negative bacteria that persistently colonize the human gastric mucosa despite the recruitment of immune cells. The H. pylori vacuolating cytotoxin (VacA) recently has been shown to inhibit stimulation-induced proliferation of primary human CD4(+) T cells. In this study, we investigated effects of VacA on the proliferation of various other types of primary human immune cells. Intoxication of PBMC with VacA inhibited the stimulation-induced proliferation of CD4(+) T cells, CD8(+) T cells, and B cells. VacA also inhibited the proliferation of purified primary human CD4(+) T cells that were stimulated by dendritic cells. VacA inhibited both T cell-induced and PMA/anti-IgM-induced proliferation of purified B cells. Intoxication with VacA did not alter the magnitude of calcium flux that occurred upon stimulation of CD4(+) T cells or B cells, indicating that VacA does not alter early signaling events required for activation and proliferation. VacA reduced the mitochondrial membrane potential of CD4(+) T cells, but did not reduce the mitochondrial membrane potential of B cells. We propose that the immunomodulatory actions of VacA on T and B lymphocytes, the major effectors of the adaptive immune response, may contribute to the ability of H. pylori to establish a persistent infection in the human gastric mucosa.     

The C-terminally encoded, MHC class II-restricted T cell antigenicity of the Helicobacter pylori virulence factor CagA promotes gastric preneoplasia

Chronic infection with the human bacterial pathogen Helicobacter pylori causes gastritis and predisposes carriers to an increased gastric cancer risk. Consequently, H. pylori-specific vaccination is widely viewed as a promising strategy of gastric cancer prevention. H. pylori strains harboring the Cag pathogenicity island (PAI) are associated with particularly unfavorable disease outcomes in humans and experimental rodent models. We show in this study using a C57BL/6 mouse model of Cag-PAI(+) H. pylori infection that the only known protein substrate of the Cag-PAI-encoded type IV secretion system, the cytotoxin-associated gene A (CagA) protein, harbors MHC class II-restricted T cell epitopes. Several distinct nonoverlapping epitopes in CagA's central and C-terminal regions were predicted in silico and could be confirmed experimentally. CagA(+) infection elicits CD4(+) T cell responses in mice, which are strongly enhanced by prior mucosal or parenteral vaccination with recombinant CagA. The adoptive transfer of CagA-specific T cells to T cell-deficient, H. pylori-infected recipients is sufficient to induce the full range of preneoplastic immunopathology. Similarly, immunization with a cholera toxin-adjuvanted, CagA(+) whole-cell sonicate vaccine sensitizes mice to, rather than protects them from, H. pylori-associated gastric cancer precursor lesions. In contrast, H. pylori-specific tolerization by neonatal administration of H. pylori sonicate in conjunction with a CD40L-neutralizing Ab prevents H. pylori-specific, pathogenic T cell responses and gastric immunopathology. We conclude that active tolerization may be superior to vaccination strategies in gastric cancer prevention.     

Cross-primed CD8+ cytotoxic T cells induce severe Helicobacter-associated gastritis in the absence of CD4+ T cells

BACKGROUND: Although previous studies have reported important roles of CD4(+) type 1-helper T cells and regulatory T cells in Helicobacter-associated gastritis, the significance of CD8(+) cytotoxic T cells remains unknown. To study the roles of CD8(+) T cells, we examined the immune response in the gastric mucosa of Helicobacter felis-infected major histocompatibility complex (MHC) class II-deficient (II(-/-)) mice, which lack CD4(+) T cells. MATERIALS AND METHODS: Stomachs from H. felis-infected wild-type and infected MHC II(-/-) mice were examined histologically and immunohistochemically. Gastric acidity and serum levels of anti-H. felis antibodies were measured. The expression of pro-inflammatory and anti-inflammatory cytokine, Fas-ligand, perforin, and Foxp3 genes in the gastric mucosa was investigated. RESULTS: H. felis-infected MHC II(-/-) mice developed severe gastritis, accompanied by marked infiltration of CD8(+) cells. At 1 and 2 months after inoculation, mucosal inflammation and atrophy were more severe in MHC II(-/-) mice, although gastritis had reached similar advanced stages at 3 months after inoculation. There was little infiltration of CD4(+) cells, and no Foxp3-positive cells were detected in the gastric mucosa of the infected MHC II(-/-) mice. The expression of the interleukin-1beta and Fas-ligand genes was up regulated, but that of Foxp3 was down regulated in the infected MHC II(-/-) mice. Serum levels of anti-H. felis antibodies were lower in the infected MHC II(-/-) mice, despite severe gastritis. CONCLUSIONS: The present study suggests that cross-primed CD8(+) cytotoxic T cells can induce severe H.-associated gastritis in the absence of CD4(+) helper T cells and that Foxp3-positive cells may have an important role in the control of gastric inflammation.